using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var text = "<span class=\"kanji-1-up kanji\">ま</span><span class=\"kanji-2-up kanji\">ちが</span><span></span>";
    	var textArray = Regex.Matches(text, @"(?s)<span(?:\s+[^>]*)?>(.*?)</span>")
    		.Cast<Match>()
    		.Select(x => x.Groups[1].Value);
        foreach (var item in textArray)
        	Console.WriteLine($"'{item}'");
	}
}